DESCRIPTION: The major objective of Dr. Yun Yen's proposal is to understand the gene structure and function of ribonucleotide reductase (RR) and its role in hydroxyurea (HU)-associated resistance. HU is a simple chemotherapeutic chemical that inhibits the M2 subunit of RR. An HU-resistant phenotype has been associated with M2 overexpression. Specific Aim 1 is to clone the genomic DNA segments containing the M1 and M2 genes from wild type and HU-resistant KB cells. Specific Aim 2 is to study the promoter and 5' flanking regions. Specific Aim 3 has the aim of examining the role of 9 critical amino acids that may play a mechanistic role in HU resistance. Specific Aim 4 will focus on the development of novel RR inhibitors, and HU/nucleoside combinations to circumvent HU resistance. These studies should lead to a substantially improved understanding of RR genetic structure and mechanism of HU resistance, and also to the development of new HU analogs capable of overcoming HU resistance.